contingency vs happening

contingency

noun
  • A possibility; something which may or may not happen. A chance occurrence, especially in finance, unexpected expenses. 

  • An amount of money which a party to a contract has to pay to the other party (usually the supplier of a major project to the client) if he or she does not fulfill the contract according to the specification. 

  • The quality of being contingent, of happening by chance. 

  • A statement which is neither a tautology nor a contradiction. 

happening

noun
  • Something that happens. 

  • A spontaneous or improvised event, especially one that involves audience participation. 

adj
  • Trendy, up-to-the-minute. 

  • Busy, lively; vibrant, dynamic; fashionable. 

How often have the words contingency and happening occurred in a corpus of books? (source: Google Ngram Viewer )